西南交通大学学报

Influence of Local Stress Variance on Elastic Stability of Compression Bar

LI Xiaozhen, XIAO Jun, LIU Dejun, LIU Chenguang, ZHANG Jingfeng, XIAO Lin

2015, 28(6): 971-976. doi: 10.3969/j.issn.0258-2724.2015.06.001

[Abstract](790)

Abstract:
To discuss how the elastic stability of compression bar is affected by local stress variances with different loading patterns, the finite element (FE) method was adopted to study the stability performance of compression under the single-point loading and surface loading. A 2-D plane beam was taken as an example and the influence of loading pattern on the local stress variance in the beam element was studied by adjusting the elements near the loading end in the geometric stiffness matrix, and eigenvalue equation was then solved. The results show that different loading patterns notably affect the critical elastic stability loads of compression bar with one end free, but has less effect on the critical loads for the constrained direction of loading end. For the compression bar with one end fixed and one end free and the slenderness ratio from 50 to 280, the critical load under surface loading is 2.14 times higher than that under singe-point loading.

Experimental Study and Prediction Model for Concrete Creep in Ambient Environment

YANG Yongqing, LU Weiwei, LI Xiaobin, YU Xiaohua

2015, 28(6): 977-983,1010. doi: 10.3969/j.issn.0258-2724.2015.06.002

[Abstract](872)

Abstract:
In order to accurately predict structural concrete creep, utilizing the benchmark creep coefficient under constant temperature and humidity, temperature creep coefficient and moisture creep coefficient were introduced to develop the combination creep model for concrete exposed to the actual ambient environment. Based on creep theory, a practical method to calculate additional creep caused by variable ambient temperature was provided. The results indicate that due to the time-varying ambient temperature and relative humidity, there is a marked difference between the actual creep and model predicted creep. The additional creep is subject to seasonal cycle variation. The relative deviation between the experimental and calculated results of combination creep model is 6%, which is reduced by 7% in contrast to the closest results by the current creep model.

Mechanical Performance Analysis of Reinforced Soil Walls with Flexible/Rigid Facings

LIU Junxiu, CHEN Jianfeng

2015, 28(6): 984-992. doi: 10.3969/j.issn.0258-2724.2015.06.003

[Abstract](849)

Abstract:
A three-dimensional numerical modelling of a reinforced soil retaining wall (RSW) with flexible/rigid facings was established based on the results of centrifugal model tests. The influence of different anchor embedded depths, anchor stiffness, vertical spacing of anchor layers,reinforcement stiffness, reinforcement length, and wall height on the mechanical performance of the wall under the surcharge loads was analyzed. The results show that the bearing ratio by the anchors is little affected by anchor embedded depth, reinforcement stiffness, anchor layer spacing, and reinforcement length, but increases significantly with the anchor stiffness. The horizontal forces acting on the combined wall facings increase with the wall height and can be calculated according to the Rankine active earth pressure theory. When the wall is under working stress conditions, the load undertaken by the anchors increases with the ratio of the anchor stiffness to the reinforcement stiffness, and when the stiffness ratio exceeds 8.6, the bearing ratio by the anchors reaches about 60% and then tends to be stable.

Experimental Study on Shear Strength Characteristics of Irregular Rock Mass Discontinuities

ZHANG Julian, SHEN Mingrong, LIANG Zhirong

2015, 28(6): 993-1000. doi: 10.3969/j.issn.0258-2724.2015.06.004

[Abstract](730)

Abstract:
To study on mechanical properties of irregular discontinuities in rock mass engineering, conventional shear tests under different normal stress were carried out with No.1, 4, 6, 8, 10 standard discontinuities proposed by Barton, and simulated with cement mortar specimens. Based on experimental data analysis, shear characteristics and shear dilatancy phenomenon are analyzed in depth. Besides, an empirical shear strength formula and an arc tangent equation of discontinuity shear properties are put forward. Results show that, cutting failure effect is more likely to take place when roughness coefficient or normal stress is higher; dilatancy phenomenon is prone to emerge along with the increase of roughness coefficient or the decrease of normal stress.

Cable-Beam Vibration Characteristics of Cable-Stayed Bridge under External Excitations

WANG Tao, SHEN Ruili

2015, 28(6): 1001-1010. doi: 10.3969/j.issn.0258-2724.2015.06.005

[Abstract](788)

Abstract:
To understand the effect of external excitations on the cable-beam vibration of large-span cable-stayed bridge, firstly, the theoretical equation for the large-amplitude cable vibration was built, and based on nonlinear vibration theory, the dynamic cable element was developed using finite element method(FEM). Secondly, a large cable-stayed bridge FEM modal was built, and the cables of the bridge were simulated by cable dynamic element. Finally, a typical cable-stayed bridge was used as an example to investigate the cable-beam vibration characteristics under different external excitations. The results indicate that it is more reasonable to study the cable-beam vibration on global bridge scale. In cable-beam vibration, there is an energy transfer process. Under external excitations, 1:1 main resonance more easily occurs than 2:1 parametric resonance. The shorter cables close to the towers in cable-stayed bridge are difficult to experience large-amplitude vibration. parametric resonance, main resonance of cable occur more easily. The shorter cables which near by the towers in cable-stayed bridge are difficult to occur large amplitude vibration.

Fatigue Evaluation Approaches of Welded Joints on Orthotropic Steel Bridge Deck

CUI Chuang, LIU Yiming, LIAO Guixing, ZHANG Qinghua, BU Yizhi

2015, 28(6): 1011-1017. doi: 10.3969/j.issn.0258-2724.2015.06.006

[Abstract](761)

Abstract:
The traditional fatigue evaluation approach for orthotropic steel bridge deck is not sufficiently accurate. To accurately evaluate the fatigue properties of welded joints on a orthotropic steel bridge deck, the validities and accuracies of the structural stress method and the notch stress method were investigated based on the liner cumulative damage theory. By taking a typical orthotropic steel bridge deck as an investigated subject, the evaluation methods were discussed by a full-scale segment model test and numerical analysis, and they were verified by the data from the existing full-scale model fatigue tests. The research results indicate that compared with the structural stress method, the notch stress method and the traditional fatigue evaluation approach have high data scatters. The structural stress method may be suitable to the fatigue evaluation of welded joints on a orthotropic steel bridge deck under the condition that the data scatter of a master S-N curve is three times of standard deviation.

Precise and Approximate Methods to Calculate Shrinkage and Creep Effects of Simply-Supported Composite Beam

ZHOU Donghua, HAN Chunxiu, YANG Tianyuan, YANG Yingen, WANG Yongshuang

2015, 28(6): 1018-1024. doi: 10.3969/j.issn.0258-2724.2015.06.007

[Abstract](721)

Abstract:
To provide a simple and feasible calculation method, differential equations for composite beam with creep and shrinkage were derived and solved based on the Dischinger's method by using exact and approximate methods respectively. When the exact method is adopted, the coupled differential equations need to be solved, the solution is difficult to acquire and too complex to apply. When the approximate method is used, the effect of moment redistribution in concrete slab on axial strain is neglected, this makes the differential equations decoupled and easy for solving. The calculation results of the two methods have a good agreement in the case of the rigidity ratio of concrete slab to steel beam being smaller than 0.2, and the error is within 2%. The larger the rigidity of steel beam, the larger the creep restrain to concrete slab and the redistribution internal forces. Furthermore, a special creep stress zero point exists in the section of steel beam.

State-of-the-Art of Dynamic Seismic Reliability Theories of Structures

LÜ, Dagang, SONG Pengyan, YU Xiaohui, QIAO Yumeng

2015, 28(6): 1025-1038. doi: 10.3969/j.issn.0258-2724.2015.06.008

[Abstract](873)

Abstract:
The state-of-the-art of theories on dynamic seismic reliability of structures is systematically reviewed from three aspects: state variable models, basic variable models, and pragmatic simplified models. For the state variable models, using the random vibration theory, methodologies for random vibration analysis are classified into two categories: One is the statistical-characteristics oriented methods, which deal with the problems of evolution of statistical moments from the space of basic random variables into the space of the state variable; another is the probability-density oriented methods, which cope with the problems of evolution of probability density from the space of basic random variables into the space of the state variable. Two representative methods of the two categories, namely the statistical linearization approach and the probability density evolution method, are critically discussed. For the basic variable models, the methods for analysis of dynamic seismic reliability of structures that take into consideration the randomness in system parameters, and the theory and methods of transformation from the dynamic reliability problems into static ones, are summarized; then, a comparison analysis is made for the recently proposed methods, including the tail equivalence linearization method, the subset simulation, and the equivalent extreme events method. For the pragmatic simplified models, three methodologies are reviewed, including the direct approach based on stochastic ground motion simulation and deterministic time-history analysis, the simplified approach based on the uniform-hazard response spectrum and equivalent nonlinear systems, and the semi-analytical approach based on simplified analytical formulations of seismic reliability and numerical simulation. Finally, the problems existing in the recent global seismic reliability theories of structures are discussed and summarized. In addition, some suggestions are provided for input models of seismic actions, search of the main failure modes, failure criteria of structures, multiple properties of structural failure modes, and global limit state functions of structures.

Investagation and Analysis of Seismic Damage to Cultural Heritage Buildings Induced by Gorkha Earthquake, Nepal

PAN Yi, XIE Dan, YUAN Shuang, SHEN Zhongwei

2015, 28(6): 1039-1046. doi: 10.3969/j.issn.0258-2724.2015.06.009

[Abstract](718)

Abstract:
An extensive investigation was made to reveal the damage caused by the 2015 Gorkha, Nepal earthquake to the cultural heritage buildings in Kathmandu Valley. The typical seismic damages are described by classifications of brick-timber structure, masonry structure and raw-soil structure, and seismic damage levels for the three structure types of cultural heritage buildings are defined. Then, proportions of different damage levels of the three structure types were obtained by statistical classification method and the damage reasons are analyzed. The results show that the brick-timber structures were almost destroyed because of the layered and eccentric compression of load-bearing walls, the lack of connection between components and the poor integrity. The masonry structures with heavy weight and large stiffness are sensitive to the seismic disturbance and weak in the seismic performance. Meanwhile, the raw-soil structures due to the low tensile strength and the poor ductility are vulnerable in the earthquake. Finally, based on the results of the seismic damage investigation and analysis as well as the research results of the Wenchuan earthquake, Yushu earthquake and Lushan earthquake, some suggestions on seismic protection of cultural heritage buildings, such as isolating the whole building, strengthening routine repair, and pertinent research, are put forward.

Probability Density Evolution Analysis of Nonlinear Seismic Response of Structures with Random Parameters Following Different Distributions

YANG Junyi, CHEN Jianbing, LI Jie

2015, 28(6): 1047-1054. doi: 10.3969/j.issn.0258-2724.2015.06.010

[Abstract](890)

Abstract:
The randomness of structural parameters should be reasonably taken into account to assess the global performance of complex structures subjected to seismic actions. In the present paper, incorporating the generalized F-discrepancy (GF-discrepancy) based optimal point selection strategy and the probability density evolution method (PDEM), the effects of different distribution types and different coefficients of variation of the random parameters on the response of a multi-degree-of-freedom nonlinear structure with tens of random parameters are studied. The results show that the difference between the second-order moments of the structural responses with different types of distributions could be in the order of 30%. When the coefficients of variation of the basic parameters are either very small or fairly large, the effects of different types of distributions on the second-order moments of responses are relatively large, but in an opposite tendency. Therefore, there exists a range of the coefficients of variation in which the different types of distributions have little effects on the second-order moments of responses. However, the probability density functions (PDFs) of the responses are always affected considerably, even may change qualitatively by the types of distributions of the random parameters.

Effects of Jiuxiang Fracture on Abnormal Intensity in Hanyuan during Wenchuan Earthquake

LI Ping, BO Jingshan, YUAN Yifan, XIAO Ruijie, LIU Hongshuai

2015, 28(6): 1055-1060,1073. doi: 10.3969/j.issn.0258-2724.2015.06.011

[Abstract](728)

Abstract:
In order to explore the causes for abnormal intensity occurring in Hanyuan Town during the Wenchuan earthquake, a typical two-dimensional model for seismic response analyses was established based on the scientific investigation and site reconnaissance of earthquake damages in Hanyuan Town and the seismogeologic and topographic maps, and the effects of Jiuxiang fracture on abnormal seismic damage in Hanyuan Town were analyzed by the finite difference method and the transmitting boundary theory. The research results show that there is a certain effect of Jiuxiang fracture on abnormal intensity in Hanyuan Town, and the ground motion may be amplified significantly in the band of 4 to 8 Hz, the peak ground motion acceleration being increased about 9%. This frequency band is the same as the vibration frequency of buildings in Hanyuan Town. Damages can be aggravated by the increased surface ground motion and resonance effect, this is one of the main reasons of high abnormal intensity in Hanyuan Town. So a non-causative fault has certain amplification effect on surface ground motion, the effect should be considered in project location and anti-seismic designs.

Water-Rock Interaction Characteristics and Softening Mechanism of Calcareous Mudstone

WANG Zhen, SHEN Mingrong, LIU Ang

2015, 28(6): 1061-1066. doi: 10.3969/j.issn.0258-2724.2015.06.012

[Abstract](780)

Abstract:
In order to deeply research the softening mechanism of soft rock after interaction with water, cretaceous calcareous mudstone, water softening rock from a water diversion tunnel in Guyuan City, Ningxia Hui Autonomous Region, was investigated by the analysis of its mineral compositions and the test of its physical-mechanical properties. Based on the test results, the water-rock interaction characteristics of calcareous mudstone were analyzed, and variation rules of strength and deformation parameters with clay mineral content were discussed. The research results show that swelling and strength of calcareous mudstone decay rapidly after water invading. There exist natural logarithmic relationships between variations of mechanical parameters and clay mineral content. The water softening of calcareous mudstone is caused by the internal hydration swelling reaction of rock and its damage intensifying in the circulation process of water absorbing and water losing, and the softening mechanism can be described in details with the schematic diagram of water-rock interaction process.

Optimization of Nose Depth for Rigid Frog

CAO Yang, WANG Ping

2015, 28(6): 1067-1073. doi: 10.3969/j.issn.0258-2724.2015.06.013

[Abstract](744)

Abstract:
Based on wheel-rail contact relationship and dynamic interaction when wheel treads pass from wing rail to nose rail, a design and evaluation method for nose depth selection of key cross-sections was proposed to select reasonable nose depths for rigid frog. A train with LMA wheel treads passing over No.12 turnout of rigid frog in the facing move of the straight direction was taken as an example, and the optimization of nose depths was carried out by this method. The research results show that the nose depths of key cross-sections should not only satisfy the safety of wheel-load transition and the strength of nose rail, but also improve the train running stability. The smaller the nose depth, the smaller the wheel-rail interaction, which is helpful to improve the running performance, but whether the wheel-rail interaction location exceeds the scope of nose bearing capability should be taken into account. To a No.12 turnout of rigid frog, the optimal nose depths of the cross-sections with railhead widths of 20 and 50 mm should be 3 and 0 mm respectively.

Effect of Longitudinal Geometric Irregularities of Wheel and Rail on Dynamic Behavior of Metro Vehicle Driven by Linear Motor

XIONG Jiayang, CAO Yabo, WU Lei, DU Xing, XIAO Xinbiao, JIN Xuesong

2015, 28(6): 1074-1081. doi: 10.3969/j.issn.0258-2724.2015.06.014

[Abstract](705)

Abstract:
A metro vehicle-track coupling dynamic model was established to investigate the effect of geometric irregularities of wheel and rail on the dynamic behavior of linear motor vehicles, which was based on the vehicle-track coupling theory and took the linear induction motor subsystem into account. Through this model, the effect of geometric irregularities, including out-of-round wheel profiles, rail welding joints and rail corrugations, on the vehicle dynamic responses, wheel-rail forces and carbody stability were studied. The results indicates that long wavelength (more than 1 m) irregularities would change the air gap and short wavelength (less than 1 m) ones would cause fierce wheel-rail impact vibration. In addition, it should be noted especially that welding joints could cause a 1.5 times wheel-rail force increase, a 2-3 mm air gap decrease, and even wheel-rail separation.

Multi-mode Vibration Attenuation Track in Low-Frequency Domain

YANG Jizhong, ZHANG Lei, CAI Chengbiao, YAN Hua

2015, 28(6): 1082-1087. doi: 10.3969/j.issn.0258-2724.2015.06.015

[Abstract](682)

Abstract:
For the phenomenon of low-frequency environmental vibration caused by the urban rail transit, based on the extended fixed-point theory, the passive vibration controlling technology, the finite element method and the vehicle-track coupling dynamics, a design method is developed to analyze the multi-mode vibration attenuation characteristics of the passive dynamic damping floating slab track (PDD_FST) in low-frequency domain, and a coupled vehicle-PDD_FST dynamics model is established. The results show that PDD_FST could effectively suppress the resonant vibration in the range of 10-20 Hz. The greater the mass ration of the attached dynamic vibration absorber (DVA) to the PDD_FST is, the greater the insertion loss of the FST acceleration is. If the mass ratio of the DVAs controlling the 1st and 2nd order mode vibration is 0.2, the max insertion loss reaches up to 15 dB. PDD_FST has less influence on the wheelset's vibration and no influence on the car body and bogie's vibration.

Sliding Mode Control for Vehicle Following System with Stochastic Disturbances

SHI Jizhong, ZHANG Jiye, XU Xiaohui, HU Yongju

2015, 28(6): 1088-1093. doi: 10.3969/j.issn.0258-2724.2015.06.016

[Abstract](630)

Abstract:
A vehicle following system and the corresponding vehicle dynamics model were set up to verify the feasibility of applying sliding mode control in vehicle following system with stochastic disturbances. A controller for the system was designed by sliding mode control method. The stability of the control system was studied by applying vector Lyapunov function method, and the sufficient conditions for exponential mean-square stability of the system were obtained. The stochastic disturbance involved in simulation was the resistances to vehicles. Simulation results showed that in less than 5 s, the accelerations and the speeds of the following vehicles converge to that of the leading vehicle, and the vehicle spacing errors approched to less than 0.05 m.

Estimation of Longitudinal Speed of In-wheel Motor Driven Vehicle Using Fuzzy Extended Kalman Filter

WANG Zhifu, LIU Mingchun, ZHOU Yang

2015, 28(6): 1094-1099. doi: 10.3969/j.issn.0258-2724.2015.06.017

[Abstract](687)

Abstract:
In order to obtain the longitudinal speed of the in-wheel motor driven vehicle, a new estimation algorithm for the extended Kalman filter was designed based on signals of wheel speed and vehicle body acceleration. First, the discrete state equation and measurement equation of the research object were established. Then, two extended Kalman filters (EKFs), including a noise filter and an estimation filer, were designed to deal with measuring signals and estimate the vehicle's longitudinal speed, respectively. Finally, the parameters obtained by the estimation filer were adjusted through the fuzzy controller to ensure the adaptivity of the algorithm. The simulation results show that the error between the estimated speed and the actual speed was less than 2% when the road adhesion coefficient was 1.00, and the error was less than 10% when the road adhesion coefficient was 0.25.

Characteristics Analysis of Sound Radiation of Box Girder Based on Transient Boundary Element Method

YIN Qiang, CAI Chengbiao, CHEN Zhaowei

2015, 28(6): 1100-1105. doi: 10.3969/j.issn.0258-2724.2015.06.018

[Abstract](713)

Abstract:
Based on the finite element-transient boundary element method, the time-domain vibration characteristics and the acoustic radiation characteristics of a 32 m-span simply supported box girder railway bridge were analyzed. Firstly, the rail-bridge finite element model was established utilizing the finite element software ANSYS, and the wheel/rail force was obtained by the train-track-bridge interaction simulation software (TTBSIM). Then, the wheel/rail force was applied to the finite element model as the external excitation, and the vibration responses of the bridge under the dynamic loading were analyzed. Finally, the radiated noise caused by the dynamic loads was analyzed based on the boundary condition of box girder vibration response by adopting the acoustic boundary element analysis software Sysnoise. Further, the calculated results were compared with the measured ones to valid the model. The results show that when the high-speed train runs at the speed of 200 km/h, the vibration of bridge deck is significantly greater than those of the bottom plate and girder web, and the bridge deck is the main site for noise radiation. The bridge structural noise mainly falls in the range of low frequencies. With the distance increasing, the noise amplitude decreases, and the attenuation of the high-frequency noise is significantly faster than the low-frequency noise.

Characteristics of Ride Comfort and Torsion Elimination of Four-Corner Interconnected Air Suspension System

JIANG Hong, QIAN Kuan, ZHU Chao, SUN Yuzhou

2015, 28(6): 1106-1113. doi: 10.3969/j.issn.0258-2724.2015.06.019

[Abstract](676)

Abstract:
In order to improve the ride comfort and decrease the vehicle body torsion load on uneven roads, a four-corner interconnected air suspension system was proposed. Based on the engineering thermodynamics and the vehicle dynamics theory, a vehicle dynamic model equipped with the four-corner interconnected air suspension was established. Then, the model accuracy was validated by a bench test, and the full vehicle model was simulated under the Matlab/Simulink environment. The results show that when a vehicle equipped with the four interconnected air suspension runs at a low speed on a twisting road, compared to that equipped with the traditional air suspension, the vehicle body acceleration, roll angle and wheel load reduce 22.5%, 24.2% and 16.3%, respectively; the vehicle body torsion load decreases 27.8%; but the suspension dynamic stroke increases 20.6%. Moreover, the interconnection brings about more benefits as the pipe diameter increases from 0 to 10 mm. The four-corner interconnected air suspension can effectively improve the ride comfort when the vehicle speed is in the range of 10-60 km/h, and the torsion elimination characteristics will be more obvious when the speed is less than 40 km/h.

Design and Optimization of Control Strategy for Plug-in 4WD Hybrid Electric Vehicles

QIAN Lijun, QIU Lihong, XIN Fulong

2015, 28(6): 1114-1121,1129. doi: 10.3969/j.issn.0258-2724.2015.06.020

[Abstract](676)

Abstract:
In order to identify drivers' intentions, and improve the fuel economy of plug-in 4WD hybrid electric vehicles (HEVs) with their power performances guaranteed, a method for calculating the torque identification coefficient was put forward. An energy management control strategy was designed based on the engine optimal control, and the judging condition of every working mode as well as its torque distribution method was introduced. In order to avoid the inherent defects of a single optimization algorithm that the calculation time was long and it was easy to end up with a local optimal solution, design of experiment (DOE) was conducted by the method of optimal Latin-hypercube design. An approximate model was designed using the RBF (radial basis function) neural network and then optimized using the multi-island genetic algorithm. In addition, an off-line simulation was conducted to verify the optimized control strategy. The results showed that the optimized control strategy could reduce the fuel consumption per 100 km of the plug-in hybrid electric vehicle by 16.4%, without degrading the power performances. After optimization, the control strategy is validated by a hardware-in-the-loop test on dSPACE and the experimental results show that the control strategy can realize the basic energy management. What's more, with torque identification, the average velocity error is reduced by 39.9% and the fuel consumption is reduced by 8.5%.

A New Multi-kernel Discriminant Analysis

LIANG Jun, ZHANG Feiyun, CHEN Long, LI Shihao, GU Shengqiang, ZHANG Wanwan

2015, 28(6): 1122-1129. doi: 10.3969/j.issn.0258-2724.2015.06.021

[Abstract](651)

Abstract:
In order to provide effective means for pattern classification and dimension reduction and stem from the advantages of two kinds of multi-kernel namely L1-MKDA and L2-MKDA, a new type of semi-infinite-programming-based flexible multi kernel discriminant analysis method was proposed, which is based on a linear combination of the predefined kernel function, and can utilize mixed norm regularization function to balance the sparsity of kernel weights. It applys semi-infinite programming algorithm to solve the elastic multi-core discriminant analysis, and achieves nuclear self-learning through the mixed regularization. Finally, the experimental results for different data sets demonstrate that the accuracy of the proposed algorithm is 5% better than those of KDA、KDAP、KDAG、L1-MKDA、L2-MKDA and UMKDA.

Matching Characteristics between Four Kinds of Wheel Steels and U71Mn Hot-Rolled Rail

LIU Jihua, WANG Wenjian, LIU Qiyue

2015, 28(6): 1130-1136. doi: 10.3969/j.issn.0258-2724.2015.06.022

[Abstract](652)

Abstract:
In order to investigate the effect of wheel materials on the matching behaviors between wheel and rail, the MMS-2A wear test machine was used to simulate the friction and wear behavior of the wheel/rail systems made of U71Mn hot-rolled rail and four kinds of wheel materials. The wear loss was measured by an electronic analytical balance and the microstructure of wheel/rail samples were analyzed by a scanning electron microscope. The results indicate that with the carbon content of wheels increasing, the wheel hardness increases and the wheel wear loss decreases, but the wear loss of the rail samples matching with the wheels increases gradually. The attrition rate of the wheel/rail samples is related to the roughness of the wear scars: the more serious the wear is, the rougher the wear scars are. In addition, the wear mechanism is determined by the hardness ratio of wheel to rail materials. When the hardness ratio is low, the wear process is dominated by a mechanism of abrasive wear, and the wear loss is the largest. With the increase of the hardness ratio, the main wear mechanism turns into a fatigue wear and the wear loss becomes less. When the hardness ratio approaches 1.1, more serious oxidation occurs to the wheel/rail samples, and oxidative wear will dominate the wear mechanism.

Probability Analysis of Negative Phase-Sequence Current for High-Speed Railway Traction Substation Based on Measured Data

WANG Bin, ZHANG Ming, QIU Zhongcai, HAN Xudong, JIANG Xiaofeng

2015, 28(6): 1137-1142. doi: 10.3969/j.issn.0258-2724.2015.06.023

[Abstract](807)

Abstract:
In order to study the problem of current unbalance in the traction power supply system of high-speed railway, the stochastic process of loads in traction substations and the negative-phase sequence current feature of V/v connection transformers are analyzed, and a negative phase-sequence current probability model was proposed by probability theory. Using this model, the negative-sequence current of a traction substation on the Beijing-Shanghai high-speed railway was simulated and verified with the measured data. The results show that the probability distribution of the negative-sequence current obtained using the design parameters of the traction substation is consistent with the analysis results from the actual data. This proves that the proposed model can reflect accurately the negative sequence current distribution of high speed railway.

Physical Modeling of IGBT and Its Parameter Identification Method Based on Neural Network

SUN Yue, TAN Jingjing, TANG Chunsen

2015, 28(6): 1143-1149,1163. doi: 10.3969/j.issn.0258-2724.2015.06.024

[Abstract](762)

Abstract:
In order to obtain the special model of insulated gate bipolar transistor (IGBT), and realize targeted optimization of the IGBT circuit, the IGBT during its on and off state was modeled separately based on Hefner model and the transient was analyzed. Meanwhile, the model parameter identification method based on neural network optimization algorithm was proposed to obtain the physical model of a single IGBT component. Finally, the parameters of an IGBT of FGA25N120 were used as an example. By the comparison of simulation and experimental results, the goodness of fit of the model was 0.9, which verifies the correctness of the proposed physical model and the accuracy of parameters identified by neural network.

Linear Elastic Nonequivalence Force for Dynamic Flow Balance Valve in Opening and Closing Process

LI Shuxun, XU Juanjuan, FAN Yilin, XU Xiaogang, YE Chen

2015, 28(6): 1150-1155. doi: 10.3969/j.issn.0258-2724.2015.06.025

[Abstract](672)

Abstract:
In order to solve the problem that the flow rate control of a dynamic flow balance valve cannot meet the precision requirement, a dynamic model for the balance valve and the motion equation of the valve core were developed. Then, the three-dimensional flow model of the valve core with the same diameter and different diameters, both under different displacements, were solved by numerical simulation. Through comparisons in terms of the displacement error and the flow characteristic curve between the actual test and numerical simulation, the variation rule and correction factor of the linear elastic nonequivalence force were obtained, and the opening profile line was optimized. The results show that after the variable opening of the valve core is optimized by the correction factor of linear elastic nonequivalence force, the displacement error of the valve core between test and theory is reduced; the flow characteristic curve obtained by numerical simulation is consistent with the one obtained by actual test, and the flow control precision can satisfy the error requirement of less than 5%.

Extraction of Forest Density Based on Airborne LiDAR and Mean Shift Algorithms

CHEN Wei, YANG Minhua, HONG Yifeng, LI Fei

2015, 28(6): 1156-1163. doi: 10.3969/j.issn.0258-2724.2015.06.026

[Abstract](600)

Abstract:
To extract forest density, Mean Shift segmentation algorithm is explored for point clouds processing. The first step is to use the Mean Shift algorithm for the point clouds initial segmentation depended on feature vectors, bandwidth and thresholds. Feature vectors consist of three-dimensional coordinates and normal vector of the point clouds and bandwidth and thresholds are determined by statistical analysis method. The second step is to obtain canopy point clouds through the analysis of the segmented point clouds added with filtering conditions such as shrubs and weeds. The third step is to use Mean Shift algorithm to calculate forest density. With the statistical analysis of segmented the canopy point clouds in each category, the steady state points are marked as the rough locations for individual trees. Finally, the results are verified by field measured data. It is found that the average accuracy of this method could be more than 90.0%, which meets the requirements of forestry industry. In comparison with the Watershed method, the accuracy of the Mean Shift method is 92.5%, which is higher than Watershed method with 70.0% accuracy, and it can avoid the over segmentation in the Watershed method.

Traffic State Identification for Urban Expressway Based on Projection Pursuit Dynamic Cluster Model

BING Qichun, GONG Bowen, YANG Zhaosheng, LIN Ciyun, QU Xin

2015, 28(6): 1164-1169. doi: 10.3969/j.issn.0258-2724.2015.06.027

[Abstract](699)

Abstract:
In order to improve the accuracy of traffic state identification for urban expressway based on the spot traffic parameters, a traffic state identification method based on projection pursuit dynamic cluster model was proposed using the mapping relationship between spot traffic parameters and traffic state. First, the projection index function was constructed by combined use of the projection pursuit technology and the dynamic cluster method, and the shuffled frog leaping algorithm was used to optimize the projection direction. Then, the traffic state identification threshold was determined using simulation data. Finally, validation and comparative analysis were carried out using both the simulated data and measured data. Experimental results indicate that the proposed model can effectively improve the accuracy of traffic state identification. The average identification rate is 97.01% and the average false identification rate is 0.86%. The average identification accuracy of proposed method is 8.9% and 4.5% higher than the BP neural network model and the fuzzy C-means clustering model, respectively.

Road Spectrum Analysis of High-Speed Rocket Sled Rail Based on Shock Response Spectrum

DONG Longlei, ZHANG Jingjing, ZHAO Jianping

2015, 28(6): 1170-1174. doi: 10.3969/j.issn.0258-2724.2015.06.028

[Abstract](660)

Abstract:
In order to evaluate the ride comfort of the high-speed rocket sled rail, an analysis method of dynamic road spectrum based on the rail's dynamic response is presented. In this method, the rocket sled test system is regarded as a sled-rail coupling system, the rail's dynamic response is used as the excitation conditions of the rocket sled, and the road spectrum is obtained through the shock response spectrum analysis. In the rocket sled test, when the rocket sled passes a given point of the rail, the acceleration of the point on the rail is selected as the excitation of the rocket sled, and the acceleration response spectrum is established by shock response spectrum transform. Then, the acceleration response spectrum is transformed to a displacement response spectrum. Finally, using the velocity of the rocket sled on the point, the displacement response spectrum is transformed to a spatial spectrum,i.e., the dynamic road spectrum. In addition, the dynamic road spectrum as high-speed rocket sled rail input is measured and analyzed. The results show that the rail characteristics based on the dynamic road spectrum analysis are consistent with the Holloman rail characteristics; the power spectral density is between 10-10-4 mm2m and the irregularity period is concentrated between 0.01-2.50 m-1.Therefore, the dynamic road spectrum can be used as the random excitation conditions of the high-speed rocket sled.

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2015 Vol. 28, No. 6